Recently, a keyboard having an illuminating function has been disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-260478 (refer to FIG. 7) and the like. In the key structure disclosed in this Patent Document, an elastic member and a linking mechanism are disposed below a key top, and a membrane circuit board, a light guiding plate, and a base plate are disposed therebelow. In addition to the configuration in which a light emitting diode (LED) as a light emitting element is provided on the membrane circuit board, there is also disclosed a configuration in which an LED is provided on an exclusive circuit board. When the exclusive circuit board is provided, the circuit board is disposed below the base plate.
In the key switch structure disclosed in this Patent Document, when light is emitted from the LED as the light emitting element, the light is guided by the light guiding plate, and is emitted upward from the light guiding plate at a position below the key top. Accordingly, a character, a symbol, and the like on the key top are brightly illuminated.